CleanCode 7章エラー処理

1.エラーコードではなく例外を使用

public class DeviceController {
	...
	public void sendShutDown() {
		DeviceHandle handle = getHandle(DEV1);
		// 디바이스 상태를 점검한댜.
		if (handle != DeviceHandle.INVALID) {
			// 레코드 필드에 디바이스 상태를 저장한다.
			retrieveDeviceRecord(handle);
			// 디바이스가 일시정지 상태가 아니라면 종료한다.
			if (record.getStatus() != DEVICE_SUSPENDED) {
				pauseDevice(handle);
				clearDeviceWorkQueue(handle);
				closeDevice(handle);
			} else {
				logger.log("Device suspended. Unable to shut down");
			}
		} else {
			logger.log("Invalid handle for: " + DEV1.toString());
		}
	}
	...
}

public class DeviceController {
	...
	public void sendShutDown() {
		try {
			tryToShutDown();
		} catch (DeviceShutDownError e) {
			logger.log(e);
		}
	}

	private void tryToShutDown() throws DeviceShutDownError {
		DeviceHandle handle = getHandle(DEV1);
		DeviceRecord record = retrieveDeviceRecord(handle);
		pauseDevice(handle); 
		clearDeviceWorkQueue(handle); 
		closeDevice(handle);
	}

	private DeviceHandle getHandle(DeviceID id) {
		...
		throw new DeviceShutDownError("Invalid handle for: " + id.toString());
		...
	}
	...
}

2.Try-Catch-Filly文を書き出します

@Test(expected = StorageException.class)
 public void retrieveSectionShouldThrowOnInvalidFileName() {
     sectionStore.retrieveSection("invalid - file");
 }

public List<RecordedGrip> retrieveSection(String sectionName) {
     // 실제로 구현할 때까지 비어 있는 더미를 반환한다.
     return new ArrayList<RecordedGrip>();
 }

public List<RecordedGrip> retrieveSection(String sectionName) {
     try {
         FileInputStream stream = new FileInputStream(sectionName);
     } catch (Exception e) {
         throw new StorageException("retrieval error", e);
     }
     return new ArrayList<RecordedGrip>();
 }

public List<RecordedGrip> retrieveSection(String sectionName) {
     try {
         FileInputStream stream = new FileInputStream(sectionName);
         stream.close();
     } catch (FileNotFoundException e) {
         throw new StorageException("retrieval error", e);
     }
     return new ArrayList<RecordedGrip>();
 }

3.未検査の例外の使用

4.例外の意味を提供する

5.呼び出し元を考慮して例外クラスを定義する

// 1
 ACMEPort port = new ACMEPort(12);

 try {
     port.open();
 } catch (DeviceResponseException e) {
     reportPortError(e);
     logger.log("Device response exception", e);
 } catch (ATM1212UnlockedException e) {
     reportPortError(e);
     logger.log("Unlock exception", e);
 } catch (GMXError e) {
     reportPortError(e);
     logger.log("Device response exception");
 } finally {
     ...
 }
 
 // 2
 public class LocalPort {
     private ACMEPort innerPort;

     public LocalPort(int portNumber) {
         innerPort = new ACMEPort(portNumber);
     }

     public void open() {
         try {
             innerPort.open();
         } catch (DeviceResponseException e) {
             throw new PortDeviceFailure(e);
         } catch (ATM1212UnlockedException e) {
             throw new PortDeviceFailure(e);
         } catch (GMXError e) {
             throw new PortDeviceFailure(e);
         }
     }
     ...
 }

6.nullを返さない

// 1
List<Employee> employees = getEmployees();
if(employees != null) {
	for(Employee e : employees) {
		totalPay += e.getPay();
	}
}

// 2
List<Employee> employees = getEmployees();
for(Employee e : employees) {
	totalPay += e.getPay();
}

public List<Employee> getEmployees() {
	if (..직원이 없다면..)
		return Collections.emptyList();
}